Focus detection device

Abstract

A focus detection device includes line sensors which photoelectrically convert and integrate light from an object and output an image signal; monitor sensors, provided adjacent to the line sensors, which monitor an integrated value of the adjacent line sensors; a control device which amplifies an output of each monitor sensor and outputs a monitor signal, and terminates integration of the line sensor corresponding to the monitor sensor when the monitor signal reaches a predetermined termination value; and a gain adjustment device which adjusts a gain level of the control device in accordance with each integration time during integration of the line sensor. The gain adjustment device adjusts the gain level of the control device so that an appropriate integrated value of the line sensor becomes an approximately predetermined value when the monitor signal reaches the predetermined termination value regardless of the integration time.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a focus detection device suitable for a focus detection apparatus of a camera.2. Description of the Related ArtA focus detection apparatus equipped with a phase difference CCD focus detection device is provided for a conventional AF single-lens reflex camera. The CCD focus detection device includes line sensors and monitor sensors corresponding with a photographic optical system and focus detection areas. Each of the monitor sensors receives light from a photographic subject (object) in approximately the same area as that of the adjacent CCD line sensor to output a monitor signal in accordance with the amount of received light. Thereafter, the monitor signal is amplified in an auto gain controller. When the amplified monitor signal reaches a predetermined integration termination value, the integration for the corresponding CCD line sensor is terminated.However, it has been discovered that the integr...

AI Technical Summary

Benefits of technology

According to an aspect of the present invention, a focus detection device is provided, including a plurality of line sensors, each having a plurality of pixels, wherein each of the line sensors photoelectrically converts and integrates light from an object received by each of the pixels so as to output the received light as an image signal; a plurality of monitor sensors provided adjacent to the line sensors, respectively, each of the monitor sensors monitoring an integrated value of the adjacent line sensor; a control device which amplifies an output of each of the monitor sensors and outputs the amplified output as a monitor signal, and terminates integration of the line sensor corresponding to the monitor sensor when the monitor signal reaches a predetermined termination value; and a gain adjustment device which adjusts a gain level of the control device in accordance with each integration time during integration of the line sensor. The gain adjustment device adjusts the gain level of the control device so that an appropriate integrated value of the line sensor becomes an approximately predetermined value when the monitor signal reaches the predetermined termination value regardless of the integration time. According to this structure, the appropriate integrated value of the line sensor can be kept approximately constant regardless of the brightness of a photographic subject and the integration time. Therefore, an effective dynamic range of the line sensor can be efficiently used regardless of the brightness of a photographic subject.

Problems solved by technology

However, it has been discovered that the integrated value of the CCD line sensor and the monitor output of the monitor sensor are not linearly proportional to each other.

Therefore, in the case of high brightness, the integrated value of a high-brightness portion of the CCD line sensor exceeds a saturated integrated value, preventing accurate phase difference measurement.

On the other hand, in the case of low brightness, the integrated value becomes smaller than the appropriate integrated value, preventing efficient use of a dynamic range of the CCD line sensor.

As a result, a contrast cannot be obtained.

As described above, in the focus detection device using the conventional CCD line sensors, the output of the CCD line sensor sometimes becomes non-uniform depending on the brightness of the object, preventing accurate measurement.

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